A conventional variable valve mechanism varies an opening/closing timing (valve timing) of an intake valve or an exhaust valve to improve an output performance, an emission performance, and a fuel efficiency performance of an internal combustion engine for a vehicle.
For example, JP06042379A, published by the Japan Patent Office in 1994, discloses a technique of reducing an HC discharge amount by performing control to increase an overlap period between an intake valve open period and an exhaust valve open period when an engine is cold using a variable valve mechanism driven by oil pressure.